Gemini AI:
WTGT; how often might Montreal go into Black Flag conditions in one year? Ever at all?
In the context of heat stress management (using the standard military/occupational Wet-Bulb Globe Temperature (WBGT) flag system, where Black Flag conditions mean an extreme risk threshold of WBGT≥90°F or 32.2°C), Montreal experiences these conditions very rarely, but they are not entirely impossible.
HeatStress.com
1. Does it ever happen at all?
Yes, but it is exceptional.
Montreal's climate is characterized by cold winters and warm, humid summers, but true extreme WBGT values exceeding 32.2°C (90°F) are typically reserved for more tropical or deep southern continental climates.
However, during severe, highly humid heatwaves (often accompanied by intense solar radiation and stagnant air), Montreal's humidex or apparent temperature can spike dramatically. While standard meteorological forecasts track humidex rather than strict WBGT, localized athletic events or outdoor military/industrial protocols operating on WBGT metrics have occasionally hit or approached these extreme advisory thresholds during the worst heat domes.
2. How often might it happen in one year?
Average Frequency: 0 to a maximum of 1 day per year (and in most years, zero).
Probability: In a typical summer, Montreal will see several days of "Red Flag" conditions (high heat stress) or severe heat warnings (canicules), where temperatures cross 30°C to 35°C with high humidity. However, the combination of parameters required to push the composite WBGT index past the strict 32.2°C Black Flag line occurs only during rare, multi-year heat anomalies.
Even as summer temperatures trend upward due to climate shifts, true Black Flag days remain extreme outliers in southern Quebec, typically flashing only for a few peak afternoon hours during the most intense historic heat events before a cold front breaks the humidity.
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https://globalcalcs.com/en/health/wbgt-heat-stress/?utm_source=copilot.com&m=outdoor&w=25&g=35&d=32
Copilot:
Is this the same as the Feels Like values? Is it american!
Short answer: Yes — it’s basically the same concept as “Feels Like,” and yes — this chart is American.
🌡️ Heat Index vs. “Feels Like”
The chart you uploaded is the NWS Heat Index, created by the U.S. National Weather Service (NOAA).
Heat Index is the U.S. standard for calculating how hot it feels when you combine temperature + humidity.
In everyday weather apps, the “Feels Like” temperature for hot conditions is usually the Heat Index (or a very close variant of it).
So when it’s humid and your app says “Feels Like 38°C,” that’s the same idea — just converted to Celsius.
Canada’s weather services (Environment Canada) use a similar metric called Humidex, but the concept is the same:
temperature + humidity = perceived heat.
🇺🇸 Is it American?
Yes.
The chart is produced by NOAA / National Weather Service, which is a U.S. federal agency.
It uses Fahrenheit and U.S. humidity thresholds, so it’s definitely American.
🔍 Quick comparison
NWS Heat Index (USA) → used in the chart
Humidex (Canada) → similar, but calculated slightly differently
“Feels Like” → your phone’s simplified version of Heat Index/Humidex depending on region
If you want, I can convert the chart’s values to Celsius or explain the difference between Heat Index and Humidex in more detail.
How are they different?
Here’s the clean, practical breakdown, Louise — Heat Index (USA) vs. Humidex (Canada) — how they differ, why they differ, and what that means for “Feels Like.”
🌡️ 1. What each one measures
Heat Index (USA – NOAA/NWS)
Combines temperature + humidity
Based on how humidity slows sweat evaporation
Uses a complex regression formula derived from experiments on human heat stress
Expressed in °F originally (converted to °C by apps)
Humidex (Canada – Environment Canada)
Combines temperature + dew point
Dew point is a more direct measure of moisture in the air
Uses a simpler physical formula based on vapor pressure
Expressed in °C
Takeaway:
Heat Index uses relative humidity, Humidex uses dew point.
Both describe how hot it feels, but they’re calculated differently.
🔬 2. How the formulas differ
Heat Index formula (simplified idea)
A long polynomial equation using:
Temperature (°F)
Relative humidity (%)
It’s based on lab studies of human heat stress.
📈 3. Practical difference in real weather
Heat Index tends to give slightly lower numbers
Because relative humidity can be misleading — 60% humidity at 30°C feels different depending on dew point.
Humidex often gives higher “Feels Like” values
Because dew point directly measures moisture load in the air.
Example:
Temp: 30°C
Dew point: 22°C
Relative humidity: ~65%
Heat Index might say: 36°C
Humidex might say: 38–40°C
So in Canada, your weather app often feels “more dramatic” because Humidex inflates the number more.
📱 4. What your phone shows as “Feels Like”
In Canada: usually Humidex
In the USA: usually Heat Index
Some apps (AccuWeather, Weather Underground): use their own proprietary “RealFeel” or “Feels Like” that includes wind, sun angle, cloud cover, etc.
But for hot weather, the “Feels Like” is almost always Heat Index or Humidex depending on country.
🧭 5. Which one is better?
Depends on what you want:
Heat Index
Better for understanding health risk
Based on human heat stress experiments
Used for official warnings in the U.S.
Humidex
Better for describing how oppressive the air feels
Dew point is a more accurate measure of moisture
Often gives higher numbers
⭐ Bottom line
Yes, they both represent “Feels Like.”
No, they are not calculated the same way.
Heat Index is American; Humidex is Canadian.
Humidex usually feels higher because it uses dew point.
If you want, I can convert the chart you uploaded into Humidex equivalents or show you how to estimate Humidex from your local dew point.
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